It's understandable that U.S. auto makers are nervous about the prospect of having to sell luxury cars that are diminutive in size, as public perception has not yet caught up with the reality of urban congestion and the energy crisis. It's even more of a problem when your name is Cadillac, a brand that is synonymous with acres of bonnet, aircraft-sized motors and enough interior room for an entourage. So it's not surprising that Cadillac's Urban Luxury Concept is a technological tour de force, with every creature comfort imaginable, or that the press release reads like an apology.